Local Heating of Oxygen Ions in the Presence of Magnetosonic Waves: Possible Source for the Warm Plasma Cloak?
S. C. Hill, N. Buzulukova, S. A. Boardsen, Mei‐Ching Fok
Abstract
Abstract In the energy regime between the plasmasphere (a few eV) and the ring current (greater than 1 keV), there exists another magnetospheric particle population with energies from a few eV to a few keV, the origins of which are debated. Studies explore generation mechanisms for warm plasma energies in the inner magnetosphere through two observed phenomena: the warm plasma cloak and the oxygen torus. The relations between these two populations are unclear. Recent data reveal local heating of cold H+ and He+ ions to warm plasma energies by magnetosonic waves. In this study, we report first observations of thermal O+ heating by magnetosonic waves and link the heating to a possible formation mechanism for the warm plasma cloak. The O+ heating is observed by different plasmaspheric density profiles, including density channels. We observe that O+ heating always occurs with thermal H+ and He+ heating. We investigate the harmonic structure of the observed magnetosonic waves and find intense O+ heating is accompanied by discrete heavy ion gyroharmonics. We suggest that locally heated thermal ions to 100s eV by magnetosonic waves along the plasmapause could provide a possible mechanism for warm plasma cloak generation.